HEK-combi-screw piles - Vroom Funderingstechnieken
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HEK-combi-screw piles

HEK combi piles are used in underground construction in tunnels, underground car parks and other such projects, in which the pile caps are installed under ground level. The same features and geotechnical bearing capacity as for HEK piles apply to HEK combi piles.

Depending on the type of pile driver, HEK combi piles can be produced in lengths of up to around 48 metres. The screw piles are formed with the help of a steel tube that is drilled into the ground.


  • HEK combi piles have a pre-fab concrete element that has to be placed underground from a higher level.
  • The pre-fab concrete element of pre-stressed concrete can absorb both compressive force and tensile strain.
  • VGS-combi piles displace earth, so only small amounts of drilled earth come to the surface.
  • Installation of the pile system is both low-noise and vibration-free.


  • HEK combi piles are highly suited to underground construction. This includes underground car parks, cellars and tunnel structures.
  • HEK combi piles, like the HEK pile system, are suitable for the foundations of projects in a built-up area, or where displaced earth coming to the surface or vibrations are unwanted.

Special aspects

Vroom Funderingstechnieken can advise you on the use of HEK combi piles, and the most appropriate type, for any sort of ground.

Monitoring during formation of the pile 

Thanks to the automatic moment of torque registration, pull-down force and drilling time, the operator has access at all times to up-to-date information on the pile being formed and can flag discrepancies in the nature of the ground or take appropriate action. Moment of torque, insertion speed and friction coefficient serve as an indication for adhering to the sounding; water ingress in the screwed tube is monitored using a plumb line or stone.

After formation (optional) 

Our own quality-control procedure allows us to respond properly to any doubts on the quality of the piles, or to customer requirements relating to implementation. Vibrated HEK combi piles made by Vroom Funderingstechnieken may be acoustically audited and assessed by an independent firm of engineering consultants.

Checking grout quality by drilling into and testing concrete cores

The grout is obtained from certified concrete mixing plants. The pre-fab concrete elements are produced and supplied by certified manufacturers. Vroom Funderingstechnieken produces HEK combi piles using a proprietary process devised as part of internal quality control and in line with nationally-applicable standards.

Allow us to advise you 

We at Vroom Funderingstechnieken prepare our leaflets and website with the greatest possible care and attention. However, no rights can be derived from such content. If you use information from our leaflets or our website without verification or further advice, this is at your own risk.

Vroom Funderingstechnieken accepts no liability for the correctness and/or suitability of the information for the purpose you envisage. Should you have any questions about the use of our products for actual projects we advise you to contact our sales department.

Technical specifications


  • Raking piles available on request, depending on situation and pile length.  
  • Available equipment: concrete pump, loader and bucket.  Machine noise level c. 90 dB. 
  • The system can be considered to be vibration-free.

Drilling rig

Continuously regulated, depending on the hydraulic drill attachment: 

  • Moment of torque 250 - 500 kNm 
  • Pull down 150 - 400 kN.

Grout injection

VGS-combi piles can be formed with grout injection if required for the integrity of the structure or where the work requires this.

Pre-fab concrete element

The pre-fab concrete element has a lifting eye in the pile cap and is bevelled on each side. The pre-fab concrete core may be delivered ex-works with profiling or a cast bar anchor.


Grout strength 25 - 35 N/mm2. Grout is inserted with a bucket or injected with a concrete pump without being pressurised. The pressure in the tube is the static pressure. When grout is used, a calculated amount of grout is inserted/injected, before the tube is topped-up with water.

Bearing capacity

Geotechnical bearing capacity as per Eurocode 7 (NEN 6743).

The screw point is a welded constructed point, adapted to the particular geotechnical circumstances. In some cases the point is cast rather than welded. The ratio of foot-shaft is optimised to Dfoot< √ 1.5 x Dshaft.

The load-bearing coefficients to be used are those stated in Eurocode 7 (NEN 6743) and the pile toe level is the bottom of the screwed-in tube.

Pile base coefficient
αp = 0.9
β= 1.0 (Dfoot< √ 1.5 x Dshaft)
S = 1.0

Bearing pile shaft friction 
αs = 0.009 (αs = 0.009 when using grout injection) 

Shaft friction when using tension piles 
αt = 0.009 (αt = 0.009 when using grout injection)

Load/deformation behaviour 
As per Eurocode 7 (NEN 6743, part 1, fig. 6 and 7).

Load spectrum 
Depending on the diameter and the nature of the ground: 

  • up to approx. 2500 kN (calculation value).
  • In specific projects, greater stresses are possible in consultation with the geotechnical advisor and Vroom Funderingstechnieken.

Structural aspects

Available tube diameters, dimensions in mm: Shaft (diameter of toe)

  • Square, 220 mm 380/450 mm   
  • Square, 250mm 410/500 mm   
  • Square, 290 mm or octagonal, 365mm 460/560 mm   
  • Square, 320 or 350 mm or octagonal, 430mm 530/650 mm  

Other diameters available on request. Maximum pile length is approx. 48 metres, depending on the diameter and nature of the ground. Longer pile lengths will be considered on request.


Vervaardigingsproces schroefpalen type VGS-combi 

  1. Positioning of steel tube, plus separate, sealing screw point. 
  2. The drill head and cutting point are correctly positioned at ground level. 
  3. The hydraulic drilling rig uses the pull-down force to screw in the tube to the correct depth. 
  4. Once the tube has reached the correct depth, the pre-fab concrete element is inserted. 
  5. Grout mortar is deposited in the tube using the bucket. The tube is then removed by vibrating or unscrewing, where the screw point and the pre-fab element, encircled by grout, remain in place. 
  6. The machine is then moved to the next position.

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Can we help you with your project?

Contact Paul Bochem. Dial +31(0)299 409 541 or send us an e-mail.

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